ML20237H301
| ML20237H301 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 08/19/1987 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20237H272 | List: |
| References | |
| NUDOCS 8708240423 | |
| Download: ML20237H301 (2) | |
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Enclosure SAFETY EVALUATION FOR V0GTLE UNIT 2 DELETION OF ELECTRICAL PENETRATION FILTER AND EXHAUST SYSTEM By "05000424/LER-1987-020, :on 870430,during Feedwater Flow Transfer While in Mode 2,feedwater Isolation Occurred on hi-hi Level Trip in Steam Generator.Caused by Main [[system" contains a listed "[" character as part of the property label and has therefore been classified as invalid. Regulating Valve Leak.Valve Recalibr|letter dated June 1,1987]], the applicant transmitted a propos_ed, revision to Sections 1.3, 3.2, and 9.4 of the Vogtle Units 1 and 2 FSAR. The proposed re-vision deletes the Electrical Penetration Filter and Exhaust (EPFE) system from Vogtle Unit 2.
The Vogtle Unit 1 EPFE system is not affected.
The EPFE system is designed to maintain a minimum negative pressure on the electrical penetration area of the control building and minimize release of airborne radioactivity following postulated post-loss-of-coolant (LOCA) con-tainment leakage by filtering potentially contaminated air from the electrical
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penetration area. The system consists of two 100 percent capacity filtration q
trains each designed to filter up to 6000 cfm.
Section 6.5.1 of the Vogtle Safety Evaluation Report (SER) described the EPFE system as an engineered safety feature (ESF) system, and credited its charcoal adsorbers with 99 percent removal efficiency for all forms of radiofodine.
However, in a subsequent meeting with the applicant on November 17, 1986, the staff was infonned that the indicated removal efficiency for the charcoal adsorbers in the EPFE system was not used in the calculations of either post-accident (LOCA) offsite radiation dose exposures per 10 CFR Part 100, or radiation exposures to operating personnel in the control room per the dose guidelines of GDC 19 On this basis, the staff accepted the applicant's j
proposal to delete the 1/8 inch negative pressure requirement from the Vogtle Unit 1 Technical Specification and to reclassify the EPFE system to a non-ESF system from an ESF system. As discussed in a telephone conference call on June 18, 1987, the applicant agreed to clarify FSAR Section 9.4.5 to clearly indicate that the Vogtle EPFE is a non-ESF system.
The electrical penetration area is normally served by the control building levels A and B normal (heating, ventilation, and air conditioning) HVAC system which has no cor.nections to either the control room normal or emergency HVAC 3
j systems, or the Technical Support Center (TSC) HVAC system.
The Vogtle con-trol room and TSC are located on level 1 in the control building above levels 1
A and B.
Following a design basis LOCA, potentially contaminated outside air is intro-duced into the control room through the control room emergency filtration system to remove radioactivity and to pressurize the control room. The out-side air is also drawn into the control building levels A and B normal HVAC system for makeup air but it is not filtered.
Deletion of the Unit 2 EPFE system could potentially increase airborne radioactivity concentrations at control building levels A and 8 due to leakage through the electrical penetrations.
As indicated above, the staff previously did not use the airborne radioactivity removal efficiencies assigned to the EPFE system in the calculations of post-LOCA offsite radiation consequences or radiation exposure to operating personnel in the control room. To evaluate the effects of deletion of the Unit 2 EPFE 8708240423 870819 ADOCK0500g5 PDR
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~ b system, the staff assumed inleakage of uhfiltered contaminated air into the control room envelope from control building levels A and B through doorways on ingress and egress, and from the control room emergency HVAC recirculation ductwork. The staff assumed 10 cfm unfiltered infiltration of contaminated air
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from control building levels A and B into the control room through doorways on ingress and egress as delineated in the guidelines of Standard Review Plan (SRP)
Section 6.4.
This assumption is conservative since the Vogtle control room is provided wi'.h a two-door vestibule type entry into the contrcl room.
This type of entry design significantly reduces contaminated air backflow into the pressurized control room.
The applicant provided a calculated comparison of airborne radioactivity concen-tration outside the control building to that inside the control building on levels A and B with a maximum total design leakage of 27 cubic centimeters per minute from 72 electrical penetrations. The results of this calculation indi-cated that the concentration inside the control building on levels A and B will be approximately 15 percent higher than outside the control building at 30 days post-LOCA due to the assumed electrical penetration leaks. The 15 percent higher concentration of airborne radioactivity at control building levels A and B due to the potential leaks from the electrical penetrations will reduce the iodine protection factor. for control room doses by 1.06 (6 percent) based on the assumed 10 cfm unfiltered air infiltration.
Using this factor, the staff calculated thyroid and whole-body doses to the control room operators to still be within the guidelines of GDC 19.
The control room emergency filtration system contains two 100 percent capacity air filtration units each designed to filter 25,000 cfm.
Each unit includes a 4 inch-deep charcoal adsorber, a control room return air fan, and a control room air filter unit fan. Upon receipt of a control room isolation signal, the control room emergency filtration system will be actuated, and the normal air handling unit will be automatically tripped. Outside air required for control room pressurization is mixed with return air upstream of the filtration unit. Air within the control room envelope is recirculated continuously through the emergency filtration unit.
The system design provides no potential bypass pathways around the emergency filtratior units.
The staff has credited the system with 99 percent removal efficiency for all forms of radiciodine.
The control room return air fan takes air from the control room envelope and the outside makeup air line and delivers it to the filtration unit. The con-trol room filter unit fan is located adjacent to the filter housing and blows air directly into the control room envelope. Any air inleakage into the system ductwork will be filtered through the 4 inch-deep charcoal adsorber prior to entering the control room envelope.
The staff, therefore, assumed no unfiltered infiltration of contaminated air from control building levels A and B into the control room through the control room emergency HVAC recirculation ductwork.
Thus, the staff finds that the slightly higher (15 percent increase) airborne radioactivity at control building levels A ana B due to post-LOCA electrical penetration leaks will not exceed the control room operator dose guidelines of GDC 19 as indicated in the guidelines of SRP Section 6.4 Based on the above, the staff concludes that the applicant's request to delete the EPFE system from Vogtle Unit 2 is acceptable since the staff's previous conclusions stated in SER Sections 6.4 and 15.6.5 are not affected, and the requirements of GDC 19 continue to be satisfied.
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